arch/arm64/mm/mmu.c

   1 /*
   2  * Based on arch/arm/mm/mmu.c
   3  *
   4  * Copyright (C) 1995-2005 Russell King
   5  * Copyright (C) 2012 ARM Ltd.
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18  */
  19
  20 #include <linux/export.h>
  21 #include <linux/kernel.h>
  22 #include <linux/errno.h>
  23 #include <linux/init.h>
  24 #include <linux/libfdt.h>
  25 #include <linux/mman.h>
  26 #include <linux/nodemask.h>
  27 #include <linux/memblock.h>
  28 #include <linux/fs.h>
  29 #include <linux/io.h>
  30 #include <linux/slab.h>
  31 #include <linux/stop_machine.h>
  32
  33 #include <asm/cputype.h>
  34 #include <asm/fixmap.h>
  35 #include <asm/sections.h>
  36 #include <asm/setup.h>
  37 #include <asm/sizes.h>
  38 #include <asm/tlb.h>
  39 #include <asm/memblock.h>
  40 #include <asm/mmu_context.h>
  41
  42 #include "mm.h"
  43
  44 u64 idmap_t0sz = TCR_T0SZ(VA_BITS);
  45
  46 /*
  47  * Empty_zero_page is a special page that is used for zero-initialized data
  48  * and COW.
  49  */
  50 struct page *empty_zero_page;
  51 EXPORT_SYMBOL(empty_zero_page);
  52
  53 pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
  54                               unsigned long size, pgprot_t vma_prot)
  55 {
  56         if (!pfn_valid(pfn))
  57                 return pgprot_noncached(vma_prot);
  58         else if (file->f_flags & O_SYNC)
  59                 return pgprot_writecombine(vma_prot);
  60         return vma_prot;
  61 }
  62 EXPORT_SYMBOL(phys_mem_access_prot);
  63
  64 static void __init *early_alloc(unsigned long sz)
  65 {
  66         void *ptr = __va(memblock_alloc(sz, sz));
  67         BUG_ON(!ptr);
  68         memset(ptr, 0, sz);
  69         return ptr;
  70 }
  71
  72 /*
  73  * remap a PMD into pages
  74  */
  75 static void split_pmd(pmd_t *pmd, pte_t *pte)
  76 {
  77         unsigned long pfn = pmd_pfn(*pmd);
  78         int i = 0;
  79
  80         do {
  81                 /*
  82                  * Need to have the least restrictive permissions available
  83                  * permissions will be fixed up later
  84                  */
  85                 set_pte(pte, pfn_pte(pfn, PAGE_KERNEL_EXEC));
  86                 pfn++;
  87         } while (pte++, i++, i < PTRS_PER_PTE);
  88 }
  89
  90 static void alloc_init_pte(pmd_t *pmd, unsigned long addr,
  91                                   unsigned long end, unsigned long pfn,
  92                                   pgprot_t prot,
  93                                   void *(*alloc)(unsigned long size))
  94 {
  95         pte_t *pte;
  96
  97         if (pmd_none(*pmd) || pmd_sect(*pmd)) {
  98                 pte = alloc(PTRS_PER_PTE * sizeof(pte_t));
  99                 if (pmd_sect(*pmd))
 100                         split_pmd(pmd, pte);
 101                 __pmd_populate(pmd, __pa(pte), PMD_TYPE_TABLE);
 102                 flush_tlb_all();
 103         }
 104         BUG_ON(pmd_bad(*pmd));
 105
 106         pte = pte_offset_kernel(pmd, addr);
 107         do {
 108                 set_pte(pte, pfn_pte(pfn, prot));
 109                 pfn++;
 110         } while (pte++, addr += PAGE_SIZE, addr != end);
 111 }
 112
 113 void split_pud(pud_t *old_pud, pmd_t *pmd)
 114 {
 115         unsigned long addr = pud_pfn(*old_pud) << PAGE_SHIFT;
 116         pgprot_t prot = __pgprot(pud_val(*old_pud) ^ addr);
 117         int i = 0;
 118
 119         do {
 120                 set_pmd(pmd, __pmd(addr | pgprot_val(prot)));
 121                 addr += PMD_SIZE;
 122         } while (pmd++, i++, i < PTRS_PER_PMD);
 123 }
 124
 125 static void alloc_init_pmd(struct mm_struct *mm, pud_t *pud,
 126                                   unsigned long addr, unsigned long end,
 127                                   phys_addr_t phys, pgprot_t prot,
 128                                   void *(*alloc)(unsigned long size))
 129 {
 130         pmd_t *pmd;
 131         unsigned long next;
 132
 133         /*
 134          * Check for initial section mappings in the pgd/pud and remove them.
 135          */
 136         if (pud_none(*pud) || pud_sect(*pud)) {
 137                 pmd = alloc(PTRS_PER_PMD * sizeof(pmd_t));
 138                 if (pud_sect(*pud)) {
 139                         /*
 140                          * need to have the 1G of mappings continue to be
 141                          * present
 142                          */
 143                         split_pud(pud, pmd);
 144                 }
 145                 pud_populate(mm, pud, pmd);
 146                 flush_tlb_all();
 147         }
 148         BUG_ON(pud_bad(*pud));
 149
 150         pmd = pmd_offset(pud, addr);
 151         do {
 152                 next = pmd_addr_end(addr, end);
 153                 /* try section mapping first */
 154                 if (((addr | next | phys) & ~SECTION_MASK) == 0) {
 155                         pmd_t old_pmd =*pmd;
 156                         set_pmd(pmd, __pmd(phys |
 157                                            pgprot_val(mk_sect_prot(prot))));
 158                         /*
 159                          * Check for previous table entries created during
 160                          * boot (__create_page_tables) and flush them.
 161                          */
 162                         if (!pmd_none(old_pmd)) {
 163                                 flush_tlb_all();
 164                                 if (pmd_table(old_pmd)) {
 165                                         phys_addr_t table = __pa(pte_offset_map(&old_pmd, 0));
 166                                         if (!WARN_ON_ONCE(slab_is_available()))
 167                                                 memblock_free(table, PAGE_SIZE);
 168                                 }
 169                         }
 170                 } else {
 171                         alloc_init_pte(pmd, addr, next, __phys_to_pfn(phys),
 172                                        prot, alloc);
 173                 }
 174                 phys += next - addr;
 175         } while (pmd++, addr = next, addr != end);
 176 }
 177
 178 static inline bool use_1G_block(unsigned long addr, unsigned long next,
 179                         unsigned long phys)
 180 {
 181         if (PAGE_SHIFT != 12)
 182                 return false;
 183
 184         if (((addr | next | phys) & ~PUD_MASK) != 0)
 185                 return false;
 186
 187         return true;
 188 }
 189
 190 static void alloc_init_pud(struct mm_struct *mm, pgd_t *pgd,
 191                                   unsigned long addr, unsigned long end,
 192                                   phys_addr_t phys, pgprot_t prot,
 193                                   void *(*alloc)(unsigned long size))
 194 {
 195         pud_t *pud;
 196         unsigned long next;
 197
 198         if (pgd_none(*pgd)) {
 199                 pud = alloc(PTRS_PER_PUD * sizeof(pud_t));
 200                 pgd_populate(mm, pgd, pud);
 201         }
 202         BUG_ON(pgd_bad(*pgd));
 203
 204         pud = pud_offset(pgd, addr);
 205         do {
 206                 next = pud_addr_end(addr, end);
 207
 208                 /*
 209                  * For 4K granule only, attempt to put down a 1GB block
 210                  */
 211                 if (use_1G_block(addr, next, phys)) {
 212                         pud_t old_pud = *pud;
 213                         set_pud(pud, __pud(phys |
 214                                            pgprot_val(mk_sect_prot(prot))));
 215
 216                         /*
 217                          * If we have an old value for a pud, it will
 218                          * be pointing to a pmd table that we no longer
 219                          * need (from swapper_pg_dir).
 220                          *
 221                          * Look up the old pmd table and free it.
 222                          */
 223                         if (!pud_none(old_pud)) {
 224                                 flush_tlb_all();
 225                                 if (pud_table(old_pud)) {
 226                                         phys_addr_t table = __pa(pmd_offset(&old_pud, 0));
 227                                         if (!WARN_ON_ONCE(slab_is_available()))
 228                                                 memblock_free(table, PAGE_SIZE);
 229                                 }
 230                         }
 231                 } else {
 232                         alloc_init_pmd(mm, pud, addr, next, phys, prot, alloc);
 233                 }
 234                 phys += next - addr;
 235         } while (pud++, addr = next, addr != end);
 236 }
 237
 238 /*
 239  * Create the page directory entries and any necessary page tables for the
 240  * mapping specified by 'md'.
 241  */
 242 static void  __create_mapping(struct mm_struct *mm, pgd_t *pgd,
 243                                     phys_addr_t phys, unsigned long virt,
 244                                     phys_addr_t size, pgprot_t prot,
 245                                     void *(*alloc)(unsigned long size))
 246 {
 247         unsigned long addr, length, end, next;
 248
 249         addr = virt & PAGE_MASK;
 250         length = PAGE_ALIGN(size + (virt & ~PAGE_MASK));
 251
 252         end = addr + length;
 253         do {
 254                 next = pgd_addr_end(addr, end);
 255                 alloc_init_pud(mm, pgd, addr, next, phys, prot, alloc);
 256                 phys += next - addr;
 257         } while (pgd++, addr = next, addr != end);
 258 }
 259
 260 static void *late_alloc(unsigned long size)
 261 {
 262         void *ptr;
 263
 264         BUG_ON(size > PAGE_SIZE);
 265         ptr = (void *)__get_free_page(PGALLOC_GFP);
 266         BUG_ON(!ptr);
 267         return ptr;
 268 }
 269
 270 static void __init create_mapping(phys_addr_t phys, unsigned long virt,
 271                                   phys_addr_t size, pgprot_t prot)
 272 {
 273         if (virt < VMALLOC_START) {
 274                 pr_warn("BUG: not creating mapping for %pa at 0x%016lx - outside kernel range\n",
 275                         &phys, virt);
 276                 return;
 277         }
 278         __create_mapping(&init_mm, pgd_offset_k(virt & PAGE_MASK), phys, virt,
 279                          size, prot, early_alloc);
 280 }
 281
 282 void __init create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
 283                                unsigned long virt, phys_addr_t size,
 284                                pgprot_t prot)
 285 {
 286         __create_mapping(mm, pgd_offset(mm, virt), phys, virt, size, prot,
 287                                 late_alloc);
 288 }
 289
 290 static void create_mapping_late(phys_addr_t phys, unsigned long virt,
 291                                   phys_addr_t size, pgprot_t prot)
 292 {
 293         if (virt < VMALLOC_START) {
 294                 pr_warn("BUG: not creating mapping for %pa at 0x%016lx - outside kernel range\n",
 295                         &phys, virt);
 296                 return;
 297         }
 298
 299         return __create_mapping(&init_mm, pgd_offset_k(virt & PAGE_MASK),
 300                                 phys, virt, size, prot, late_alloc);
 301 }
 302
 303 #ifdef CONFIG_DEBUG_RODATA
 304 static void __init __map_memblock(phys_addr_t start, phys_addr_t end)
 305 {
 306         /*
 307          * Set up the executable regions using the existing section mappings
 308          * for now. This will get more fine grained later once all memory
 309          * is mapped
 310          */
 311         unsigned long kernel_x_start = round_down(__pa(_stext), SECTION_SIZE);
 312         unsigned long kernel_x_end = round_up(__pa(__init_end), SECTION_SIZE);
 313
 314         if (end < kernel_x_start) {
 315                 create_mapping(start, __phys_to_virt(start),
 316                         end - start, PAGE_KERNEL);
 317         } else if (start >= kernel_x_end) {
 318                 create_mapping(start, __phys_to_virt(start),
 319                         end - start, PAGE_KERNEL);
 320         } else {
 321                 if (start < kernel_x_start)
 322                         create_mapping(start, __phys_to_virt(start),
 323                                 kernel_x_start - start,
 324                                 PAGE_KERNEL);
 325                 create_mapping(kernel_x_start,
 326                                 __phys_to_virt(kernel_x_start),
 327                                 kernel_x_end - kernel_x_start,
 328                                 PAGE_KERNEL_EXEC);
 329                 if (kernel_x_end < end)
 330                         create_mapping(kernel_x_end,
 331                                 __phys_to_virt(kernel_x_end),
 332                                 end - kernel_x_end,
 333                                 PAGE_KERNEL);
 334         }
 335
 336 }
 337 #else
 338 static void __init __map_memblock(phys_addr_t start, phys_addr_t end)
 339 {
 340         create_mapping(start, __phys_to_virt(start), end - start,
 341                         PAGE_KERNEL_EXEC);
 342 }
 343 #endif
 344
 345 static void __init map_mem(void)
 346 {
 347         struct memblock_region *reg;
 348         phys_addr_t limit;
 349
 350         /*
 351          * Temporarily limit the memblock range. We need to do this as
 352          * create_mapping requires puds, pmds and ptes to be allocated from
 353          * memory addressable from the initial direct kernel mapping.
 354          *
 355          * The initial direct kernel mapping, located at swapper_pg_dir, gives
 356          * us PUD_SIZE (4K pages) or PMD_SIZE (64K pages) memory starting from
 357          * PHYS_OFFSET (which must be aligned to 2MB as per
 358          * Documentation/arm64/booting.txt).
 359          */
 360         if (IS_ENABLED(CONFIG_ARM64_64K_PAGES))
 361                 limit = PHYS_OFFSET + PMD_SIZE;
 362         else
 363                 limit = PHYS_OFFSET + PUD_SIZE;
 364         memblock_set_current_limit(limit);
 365
 366         /* map all the memory banks */
 367         for_each_memblock(memory, reg) {
 368                 phys_addr_t start = reg->base;
 369                 phys_addr_t end = start + reg->size;
 370
 371                 if (start >= end)
 372                         break;
 373
 374 #ifndef CONFIG_ARM64_64K_PAGES
 375                 /*
 376                  * For the first memory bank align the start address and
 377                  * current memblock limit to prevent create_mapping() from
 378                  * allocating pte page tables from unmapped memory.
 379                  * When 64K pages are enabled, the pte page table for the
 380                  * first PGDIR_SIZE is already present in swapper_pg_dir.
 381                  */
 382                 if (start < limit)
 383                         start = ALIGN(start, PMD_SIZE);
 384                 if (end < limit) {
 385                         limit = end & PMD_MASK;
 386                         memblock_set_current_limit(limit);
 387                 }
 388 #endif
 389                 __map_memblock(start, end);
 390         }
 391
 392         /* Limit no longer required. */
 393         memblock_set_current_limit(MEMBLOCK_ALLOC_ANYWHERE);
 394 }
 395
 396 void __init fixup_executable(void)
 397 {
 398 #ifdef CONFIG_DEBUG_RODATA
 399         /* now that we are actually fully mapped, make the start/end more fine grained */
 400         if (!IS_ALIGNED((unsigned long)_stext, SECTION_SIZE)) {
 401                 unsigned long aligned_start = round_down(__pa(_stext),
 402                                                         SECTION_SIZE);
 403
 404                 create_mapping(aligned_start, __phys_to_virt(aligned_start),
 405                                 __pa(_stext) - aligned_start,
 406                                 PAGE_KERNEL);
 407         }
 408
 409         if (!IS_ALIGNED((unsigned long)__init_end, SECTION_SIZE)) {
 410                 unsigned long aligned_end = round_up(__pa(__init_end),
 411                                                         SECTION_SIZE);
 412                 create_mapping(__pa(__init_end), (unsigned long)__init_end,
 413                                 aligned_end - __pa(__init_end),
 414                                 PAGE_KERNEL);
 415         }
 416 #endif
 417 }
 418
 419 #ifdef CONFIG_DEBUG_RODATA
 420 void mark_rodata_ro(void)
 421 {
 422         create_mapping_late(__pa(_stext), (unsigned long)_stext,
 423                                 (unsigned long)_etext - (unsigned long)_stext,
 424                                 PAGE_KERNEL_EXEC | PTE_RDONLY);
 425
 426 }
 427 #endif
 428
 429 void fixup_init(void)
 430 {
 431         create_mapping_late(__pa(__init_begin), (unsigned long)__init_begin,
 432                         (unsigned long)__init_end - (unsigned long)__init_begin,
 433                         PAGE_KERNEL);
 434 }
 435
 436 /*
 437  * paging_init() sets up the page tables, initialises the zone memory
 438  * maps and sets up the zero page.
 439  */
 440 void __init paging_init(void)
 441 {
 442         void *zero_page;
 443
 444         map_mem();
 445         fixup_executable();
 446
 447         /* allocate the zero page. */
 448         zero_page = early_alloc(PAGE_SIZE);
 449
 450         bootmem_init();
 451
 452         empty_zero_page = virt_to_page(zero_page);
 453
 454         /*
 455          * TTBR0 is only used for the identity mapping at this stage. Make it
 456          * point to zero page to avoid speculatively fetching new entries.
 457          */
 458         cpu_set_reserved_ttbr0();
 459         flush_tlb_all();
 460         cpu_set_default_tcr_t0sz();
 461 }
 462
 463 /*
 464  * Check whether a kernel address is valid (derived from arch/x86/).
 465  */
 466 int kern_addr_valid(unsigned long addr)
 467 {
 468         pgd_t *pgd;
 469         pud_t *pud;
 470         pmd_t *pmd;
 471         pte_t *pte;
 472
 473         if ((((long)addr) >> VA_BITS) != -1UL)
 474                 return 0;
 475
 476         pgd = pgd_offset_k(addr);
 477         if (pgd_none(*pgd))
 478                 return 0;
 479
 480         pud = pud_offset(pgd, addr);
 481         if (pud_none(*pud))
 482                 return 0;
 483
 484         if (pud_sect(*pud))
 485                 return pfn_valid(pud_pfn(*pud));
 486
 487         pmd = pmd_offset(pud, addr);
 488         if (pmd_none(*pmd))
 489                 return 0;
 490
 491         if (pmd_sect(*pmd))
 492                 return pfn_valid(pmd_pfn(*pmd));
 493
 494         pte = pte_offset_kernel(pmd, addr);
 495         if (pte_none(*pte))
 496                 return 0;
 497
 498         return pfn_valid(pte_pfn(*pte));
 499 }
 500 #ifdef CONFIG_SPARSEMEM_VMEMMAP
 501 #ifdef CONFIG_ARM64_64K_PAGES
 502 int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node)
 503 {
 504         return vmemmap_populate_basepages(start, end, node);
 505 }
 506 #else   /* !CONFIG_ARM64_64K_PAGES */
 507 int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node)
 508 {
 509         unsigned long addr = start;
 510         unsigned long next;
 511         pgd_t *pgd;
 512         pud_t *pud;
 513         pmd_t *pmd;
 514
 515         do {
 516                 next = pmd_addr_end(addr, end);
 517
 518                 pgd = vmemmap_pgd_populate(addr, node);
 519                 if (!pgd)
 520                         return -ENOMEM;
 521
 522                 pud = vmemmap_pud_populate(pgd, addr, node);
 523                 if (!pud)
 524                         return -ENOMEM;
 525
 526                 pmd = pmd_offset(pud, addr);
 527                 if (pmd_none(*pmd)) {
 528                         void *p = NULL;
 529
 530                         p = vmemmap_alloc_block_buf(PMD_SIZE, node);
 531                         if (!p)
 532                                 return -ENOMEM;
 533
 534                         set_pmd(pmd, __pmd(__pa(p) | PROT_SECT_NORMAL));
 535                 } else
 536                         vmemmap_verify((pte_t *)pmd, node, addr, next);
 537         } while (addr = next, addr != end);
 538
 539         return 0;
 540 }
 541 #endif  /* CONFIG_ARM64_64K_PAGES */
 542 void vmemmap_free(unsigned long start, unsigned long end)
 543 {
 544 }
 545 #endif  /* CONFIG_SPARSEMEM_VMEMMAP */
 546
 547 static pte_t bm_pte[PTRS_PER_PTE] __page_aligned_bss;
 548 #if CONFIG_PGTABLE_LEVELS > 2
 549 static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss;
 550 #endif
 551 #if CONFIG_PGTABLE_LEVELS > 3
 552 static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss;
 553 #endif
 554
 555 static inline pud_t * fixmap_pud(unsigned long addr)
 556 {
 557         pgd_t *pgd = pgd_offset_k(addr);
 558
 559         BUG_ON(pgd_none(*pgd) || pgd_bad(*pgd));
 560
 561         return pud_offset(pgd, addr);
 562 }
 563
 564 static inline pmd_t * fixmap_pmd(unsigned long addr)
 565 {
 566         pud_t *pud = fixmap_pud(addr);
 567
 568         BUG_ON(pud_none(*pud) || pud_bad(*pud));
 569
 570         return pmd_offset(pud, addr);
 571 }
 572
 573 static inline pte_t * fixmap_pte(unsigned long addr)
 574 {
 575         pmd_t *pmd = fixmap_pmd(addr);
 576
 577         BUG_ON(pmd_none(*pmd) || pmd_bad(*pmd));
 578
 579         return pte_offset_kernel(pmd, addr);
 580 }
 581
 582 void __init early_fixmap_init(void)
 583 {
 584         pgd_t *pgd;
 585         pud_t *pud;
 586         pmd_t *pmd;
 587         unsigned long addr = FIXADDR_START;
 588
 589         pgd = pgd_offset_k(addr);
 590         pgd_populate(&init_mm, pgd, bm_pud);
 591         pud = pud_offset(pgd, addr);
 592         pud_populate(&init_mm, pud, bm_pmd);
 593         pmd = pmd_offset(pud, addr);
 594         pmd_populate_kernel(&init_mm, pmd, bm_pte);
 595
 596         /*
 597          * The boot-ioremap range spans multiple pmds, for which
 598          * we are not preparted:
 599          */
 600         BUILD_BUG_ON((__fix_to_virt(FIX_BTMAP_BEGIN) >> PMD_SHIFT)
 601                      != (__fix_to_virt(FIX_BTMAP_END) >> PMD_SHIFT));
 602
 603         if ((pmd != fixmap_pmd(fix_to_virt(FIX_BTMAP_BEGIN)))
 604              || pmd != fixmap_pmd(fix_to_virt(FIX_BTMAP_END))) {
 605                 WARN_ON(1);
 606                 pr_warn("pmd %p != %p, %p\n",
 607                         pmd, fixmap_pmd(fix_to_virt(FIX_BTMAP_BEGIN)),
 608                         fixmap_pmd(fix_to_virt(FIX_BTMAP_END)));
 609                 pr_warn("fix_to_virt(FIX_BTMAP_BEGIN): %08lx\n",
 610                         fix_to_virt(FIX_BTMAP_BEGIN));
 611                 pr_warn("fix_to_virt(FIX_BTMAP_END):   %08lx\n",
 612                         fix_to_virt(FIX_BTMAP_END));
 613
 614                 pr_warn("FIX_BTMAP_END:       %d\n", FIX_BTMAP_END);
 615                 pr_warn("FIX_BTMAP_BEGIN:     %d\n", FIX_BTMAP_BEGIN);
 616         }
 617 }
 618
 619 void __set_fixmap(enum fixed_addresses idx,
 620                                phys_addr_t phys, pgprot_t flags)
 621 {
 622         unsigned long addr = __fix_to_virt(idx);
 623         pte_t *pte;
 624
 625         BUG_ON(idx <= FIX_HOLE || idx >= __end_of_fixed_addresses);
 626
 627         pte = fixmap_pte(addr);
 628
 629         if (pgprot_val(flags)) {
 630                 set_pte(pte, pfn_pte(phys >> PAGE_SHIFT, flags));
 631         } else {
 632                 pte_clear(&init_mm, addr, pte);
 633                 flush_tlb_kernel_range(addr, addr+PAGE_SIZE);
 634         }
 635 }
 636
 637 void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
 638 {
 639         const u64 dt_virt_base = __fix_to_virt(FIX_FDT);
 640         pgprot_t prot = PAGE_KERNEL | PTE_RDONLY;
 641         int granularity, size, offset;
 642         void *dt_virt;
 643
 644         /*
 645          * Check whether the physical FDT address is set and meets the minimum
 646          * alignment requirement. Since we are relying on MIN_FDT_ALIGN to be
 647          * at least 8 bytes so that we can always access the size field of the
 648          * FDT header after mapping the first chunk, double check here if that
 649          * is indeed the case.
 650          */
 651         BUILD_BUG_ON(MIN_FDT_ALIGN < 8);
 652         if (!dt_phys || dt_phys % MIN_FDT_ALIGN)
 653                 return NULL;
 654
 655         /*
 656          * Make sure that the FDT region can be mapped without the need to
 657          * allocate additional translation table pages, so that it is safe
 658          * to call create_mapping() this early.
 659          *
 660          * On 64k pages, the FDT will be mapped using PTEs, so we need to
 661          * be in the same PMD as the rest of the fixmap.
 662          * On 4k pages, we'll use section mappings for the FDT so we only
 663          * have to be in the same PUD.
 664          */
 665         BUILD_BUG_ON(dt_virt_base % SZ_2M);
 666
 667         if (IS_ENABLED(CONFIG_ARM64_64K_PAGES)) {
 668                 BUILD_BUG_ON(__fix_to_virt(FIX_FDT_END) >> PMD_SHIFT !=
 669                              __fix_to_virt(FIX_BTMAP_BEGIN) >> PMD_SHIFT);
 670
 671                 granularity = PAGE_SIZE;
 672         } else {
 673                 BUILD_BUG_ON(__fix_to_virt(FIX_FDT_END) >> PUD_SHIFT !=
 674                              __fix_to_virt(FIX_BTMAP_BEGIN) >> PUD_SHIFT);
 675
 676                 granularity = PMD_SIZE;
 677         }
 678
 679         offset = dt_phys % granularity;
 680         dt_virt = (void *)dt_virt_base + offset;
 681
 682         /* map the first chunk so we can read the size from the header */
 683         create_mapping(round_down(dt_phys, granularity), dt_virt_base,
 684                        granularity, prot);
 685
 686         if (fdt_check_header(dt_virt) != 0)
 687                 return NULL;
 688
 689         size = fdt_totalsize(dt_virt);
 690         if (size > MAX_FDT_SIZE)
 691                 return NULL;
 692
 693         if (offset + size > granularity)
 694                 create_mapping(round_down(dt_phys, granularity), dt_virt_base,
 695                                round_up(offset + size, granularity), prot);
 696
 697         memblock_reserve(dt_phys, size);
 698
 699         return dt_virt;
 700 }